Methods for detecting biomarkers (e.g., nucleic acids, proteins, lipids, sugar chains, and hormones) are very important for analytical diagnosis. In particular, detection methods with the use of fine particles have been gaining attention because high reaction efficiency (due to the large specific surface area) and high rates of reaction (due to motility greater than that of a bulk body) are expected to be obtained thereby.
An example of a method for detecting a specimen with the use of a fine particle is described in JP Patent Publication (Kohyo) No. 2004-501340 A. This method is a method for detecting a specimen with the use of a gold nanoparticle to which an oligonucleotide has adhered. The method involves a technique for detecting color changes that appear following aggregation of gold nanoparticles as a result of formation of a crosslinking structure comprising DNA serving as a specimen and an oligonucleotide adhering to a gold nanoparticle. However, according to this method, a crosslinking structure must be formed for detection, and thus at least two different probes are required. In addition, it is necessary to use as many specimens as particles, resulting in insufficiency in terms of the detection limit.
Further, a method for detecting a specimen with the use of an antibody as a probe, wherein formation of a sandwich structure is utilized, (e.g., immunochromatography) has been known. However, when a low-molecular-weight compound such as a hormone is used as a specimen, a sandwich structure is not formed, and thus detection is difficult.